This invention relates generally to packaging and more particularly to flexible packaging.
Flexible containers formed of sheet materials have gained wide acceptance in the trade for holding foodstuffs, chemicals, or other air perishable materials therein. One common type of flexible package container is the so-called gussetted package. That package is formed from a web of flexible stock material, e.g., polyethylene, polyester, polypropylene, metal foil, and combinations thereof in single or multiple plies, into a tubular body, having a front panel a rear panel, and a pair of gussetted sides. Each gussetted side is formed by a a pair of gusset sections and a central fold edge interposed between a pair of outer fold edges. The marginal edges of the front and rear panels form the outer fold edges. The outer fold edges of one side of both panels and the interposed central fold edge define therebetween respective gusset sections. Those sections are subadjacent (underlie) the marginal edges of their associated panels. The other gussetted side of the package is constructed in an identical manner. The lower end of many such prior art gussetted packages are commonly permanently sealed, e.g., heat sealed, along a line extending transversely across the width of the package close to the bottom edge of the package. The upper end of each such package is left open to form a mouth for filling (and in many cases, emptying) the package. Thus, it is a common practice to form the mouth of the package of sealable, (e.g., heat sealable), means to enable the package to be sealed at its mouth after the package is filled with its desired contents.
Owing to the fact that the mouth of the package is four layers thick at the marginal edges of the panels (the four layers being the marginal edges of the panels themselves and their respective subadjacent gusset sections), while being only two layers thick between the marginal edges (the two layers being the panels themselves), heat sealing the package's mouth is somewhat difficult to achieve. In particular, one cannot utilize the prior art, continuous sealing technique which is usually employed to seal the mouths of non-gussetted packages. That technique is quite efficient in that it entails moving the packages to be sealed through a sealing station so that the mouth of each package passes between an opposed pair of heated members, e.g., circulating bands, which apply heat and pressure as the packages move thereby. Unfortunately that technique frequently cannot be used to seal gussetted packages due to the inherently long dwell time/pressure necessary for a good seal through the multiple layers of a gussetted package. To obviate that problem it is an accepted technique in the prior art to seal a gussetted package's mouth by the placing of the package in a fixed position between an opposed pair of heated jaws whose length is at least as long as the width of the package to be sealed, and by bringing the jaws towards each other to apply heat and pressure to the interposed portions of the package. In some cases, e.g., depending upon the make-up of the material(s) forming the gussetted package, even that intermittent sealing technique may result in an unevenly sealed or otherwise unacceptably sealed package.
Special means may be provided at the mouth of a gussetted flexible package to facilitates its sealing and easy opening. For example, in U.S. Pat. No. 4,705,174, which is assigned to the same assignee as this invention and whose disclosure is incorporated by reference herein, there is disclosed a gussetted flexible package having a mouth portion including means to enable it to be heat sealed to hermetically hold coffee or some other air perishable material therein, while enabling that package to be readily peeled open at its mouth when it is desire to remove the contents of the package. As disclosed in that patent the mouth of the package is sealed by the use of the aforementioned intermittent sealing technique.
Notwithstanding the teachings of the aforementioned patent, the need still exists for a gussetted flexible package having an open mouth which can be readily sealed, e.g., sealed by the application of heat and pressure to the package's mouth as it is moved past a sealing station.